libc: don't needlessly add vfork.o to NOASM

[brooks]

Summary

For architectures where vfork.S was named Ovfork.S this was needed, but
it was always pointless here as an entry in either MDASM or NOASM is
equivalent.

Sponsored by: DARPA

[kib]

Are you sure about amd64? There is the arch-specific manually written vfork.S.
Does the patch rely on vfork.S in MD directory to override vfork.s automatically generated for the syscall?

[brooks]

In D42914#978872, @kib wrote:

Are you sure about amd64? There is the arch-specific manually written vfork.S.
Does the patch rely on vfork.S in MD directory to override vfork.s automatically generated for the syscall?

Yes, I'm sure. The presence of vfork.S in MDASM prevents the default stub from being generated in the same loop that handles NOASM. I'm pretty sure they only reasons these were there is that i386 put the real implementation in Ovfork.S and then porters copied it around.